1. Field of the Invention
The present invention relates to a communication terminal device which uses an SIP (Session Initiation Protocol) to perform call control and its control method, and more particularly to a communication terminal device which performs redial control by utilizing redial information sent from a called terminal through a call control procedure using the SIP and its control method.
2. Description of the Related Art
Facsimile machines generally have a function to redial for a prescribed number of times with prescribed time intervals when a call is made but the party on the called end of the line is busy.
Such a redial control function generally uses a method by which a calling terminal manages redial intervals and the number of redialing, and the redial control is performed under the leadership of the calling terminal.
As a known example of such a type of redial control, there is Japanese Patent Laid-Open Publication No. 62-274952 which manages a primary number of redialing and a secondary number of redialing by the calling terminal.
The above-described facsimile machine cannot confirm if the called terminal responds to redialing. Because, the called terminal did not have an effective unit to inform the calling terminal when the called terminal became ready to receive a call.
Meanwhile, facsimile machines using the SIP for call control are becoming increasing common in these years. The call control using the SIP can send redial information including information about when acceptance of a call becomes available from the called terminal to the calling terminal if the called terminal is busy.
When the calling terminal controls the redial intervals and the number of redialing in the same way as the conventional facsimile machines, however, redial information transmitted from the called terminal could not be used.
Therefore, the conventional mainstream of managing the redial intervals and the number of redialing by the calling terminal to control redialing is still popular, there are lots of useless redialing, and a success rate of communications is low.
As described above, the conventional facsimile machines manage the redial intervals and the number of redialing by the calling terminal, redial information sent from the called terminal through the call control procedure using the SIP cannot be used, and the redial control must be performed under the leadership of the calling terminal. Therefore, there were disadvantages that redial control was made-many times uselessly and a probability of success in communications was low.
The present invention has been made to remedy the above problems and to provide a communication terminal device which can make redial control considering incoming call acceptable conditions of the called terminal by using redial information sent from the called terminal through call control procedure using the SIP and can reduce useless redialing and improve a probability of success in communications, and its control method.